Various types of flexible couplings are described in European patent specification EP 0 041 708 A2 (Seppala), U.S. Pat. No. 4,207,758 (Stone), and U.S. Pat. No. 4,741,722 (Federn).
International patent application publication no. WO 98/07999 (Jewell) describes a flexible coupling for shafts that are nominally collinear and are to be coupled to rotate together while being subject to misalignments of different kinds. It includes at least one curved re-entrant column circumferentially spaced about the axis of rotation and individually deformable by bending or twisting or both, and therefore responsive to deformations introduced by parallel and axial shaft alignment. The composite result is that torque of a given loading is transferred uniformly from the driving to the driven member regardless of the misalignment effects since different deformations are introduced and compensated in the column or columns dependent on their instantaneous positions in the cycle of rotation. The arrangement enables meeting different load and misalignment requirements by varying the parameters of the columns, the manner in which they are coupled to the shafts, and the characteristics of the columns along their lengths. In an embodiment of this coupling comprising two curved re-entrant columns, each column contributes approximately half of the needed compensation, so that the coupling can be used where shafts misalignments are substantial. Nonetheless, the length of such a coupling is the sum of the lengths of the curved re-entrant columns and the width of the gap necessary to be formed in-between them. Furthermore, an additional element such as a sleeve is required for connecting the columns with each other.
Concerning continually increasing requirements for compactness of such flexible couplings, especially to be used in direct (in-line) design of drive systems, there is still a need for providing a flexible coupling featuring reduced axial length, which would be easy to manufacture and to assemble.